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Monte Carlo Simulations and Experimental Validation of Rapid Dose Delivery with Very High-Energy Electron Beams

M Bazalova

M Bazalova1*, P Maxim1, S Tantawi2, E Colby2, A Koong1, BW Loo1, (1) Stanford University, Stanford, CA, (2) SLAC National Accelerator Laboratory, Menlo Park, CA

WE-C-BRB-5 Wednesday 10:30:00 AM - 12:30:00 PM Room: Ballroom B

Purpose: To evaluate the feasibility to treat lung cancer with very high-energy electrons (VHEE) by Monte Carlo (MC) simulations and to estimate the beam-on time based on experimental dose measurements on an existing VHEE beam line.

Methods: Manually optimized VHEE treatment plans for a simulated lung tumor were calculated for beam energies ranging from 50 to 150 MeV in the EGSnrc/DOSXYZnrc MC code. A state-of-the-art RapidArc plan with a 6 MV photon beam was calculated for the same scenario using the Eclipse treatment planning system. The minimal electron beam energy matching the 6MV photon RapidArc plan was identified. VHEE dose from 50 and 70 MeV electrons was measured with Gafchromic EBT2 films on the Next Linear Collider Test Accelerator (NLCTA) beam line adapted to our experiments at the SLAC National Accelerator Laboratory. The experimental setup was modeled in the MCNPX code and the proton and neutron contributions to the total dose were quantified. The total treatment time for the lung case was estimated based on the parameters of the NLCTA beam line and experimental data.

Results: For the selected clinical scenario, 75-100 MeV electron beams produced plans of comparably high quality to the best photon plans. The simulated NLCTA percentage depth dose curves and beam profiles at 6 mm depth generally agreed with measurements within 5% for both energies and all beam sizes. The dose contribution from protons and neutrons was negligible, accounting for less than 1x10-2% of the maximum total dose. Based on the beam line parameters and the measurements, a dose of 10 Gy to 95% of the 8 cc PTV could be in principle delivered in 1.3 s.

Conclusions: Our results combining MC simulations with experimental measurements suggest that treatments of lung cancer with VHEE are feasible and very fast. We anticipate superior results with plan optimization.

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